linux.git/drivers/tty/serial/8250, branch v6.14

serial: 8250: Fix fifo underflow on flush

2025-02-14T08:50:55+00:00

When flushing the serial port's buffer, uart_flush_buffer() calls
kfifo_reset() but if there is an outstanding DMA transfer then the
completion function will consume data from the kfifo via
uart_xmit_advance(), underflowing and leading to ongoing DMA as the
driver tries to transmit another 2^32 bytes.

This is readily reproduced with serial-generic and amidi sending even
short messages as closing the device on exit will wait for the fifo to
drain and in the underflow case amidi hangs for 30 seconds on exit in
tty_wait_until_sent().  A trace of that gives:

     kworker/1:1-84    [001]    51.769423: bprint:               serial8250_tx_dma: tx_size=3 fifo_len=3
           amidi-763   [001]    51.769460: bprint:               uart_flush_buffer: resetting fifo
 irq/21-fe530000-76    [000]    51.769474: bprint:               __dma_tx_complete: tx_size=3
 irq/21-fe530000-76    [000]    51.769479: bprint:               serial8250_tx_dma: tx_size=4096 fifo_len=4294967293
 irq/21-fe530000-76    [000]    51.781295: bprint:               __dma_tx_complete: tx_size=4096
 irq/21-fe530000-76    [000]    51.781301: bprint:               serial8250_tx_dma: tx_size=4096 fifo_len=4294963197
 irq/21-fe530000-76    [000]    51.793131: bprint:               __dma_tx_complete: tx_size=4096
 irq/21-fe530000-76    [000]    51.793135: bprint:               serial8250_tx_dma: tx_size=4096 fifo_len=4294959101
 irq/21-fe530000-76    [000]    51.804949: bprint:               __dma_tx_complete: tx_size=4096

Since the port lock is held in when the kfifo is reset in
uart_flush_buffer() and in __dma_tx_complete(), adding a flush_buffer
hook to adjust the outstanding DMA byte count is sufficient to avoid the
kfifo underflow.

Fixes: 9ee4b83e51f74 ("serial: 8250: Add support for dmaengine")
Cc: stable 
Signed-off-by: John Keeping 
Link: https://lore.kernel.org/r/20250208124148.1189191-1-jkeeping@inmusicbrands.com
Signed-off-by: Greg Kroah-Hartman

serial: 8250_pnp: Remove unneeded ->iotype assignment

2025-02-04T13:44:53+00:00

If ->iobase is set the default will be UPIO_PORT for ->iotype after
the uart_read_and_validate_port_properties() call. Hence no need
to assign that explicitly. Otherwise it will be UPIO_MEM.

Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20250124161530.398361-7-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

serial: 8250_platform: Remove unneeded ->iotype assignment

2025-02-04T13:44:52+00:00

If ->iobase is set the default will be UPIO_PORT for ->iotype after
the uart_read_and_validate_port_properties() call. Hence no need
to assign that explicitly. Otherwise it will be UPIO_MEM.

Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20250124161530.398361-6-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

serial: 8250_of: Remove unneeded ->iotype assignment

2025-02-04T13:44:50+00:00

If ->iobase is set the default will be UPIO_PORT for ->iotype after
the uart_read_and_validate_port_properties() call. Hence no need
to assign that explicitly.

Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20250124161530.398361-5-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

Revert "serial: 8250: Switch to nbcon console"

2025-01-22T09:35:56+00:00

This reverts commit b63e6f60eab45b16a1bf734fef9035a4c4187cd5.

kernel test robot has found problems with this commit so revert it for
now.

Link: https://lore.kernel.org/r/202501221029.fb0d574d-lkp@intel.com
Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-lkp/202501221029.fb0d574d-lkp@intel.com
Cc: John Ogness 
Cc: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

Revert "serial: 8250: Revert "drop lockdep annotation from serial8250_clear_IER()""

2025-01-22T09:34:25+00:00

This reverts commit 422c9727b07f9f86e2ec11c56622e566221591cc.

kernel test robot has found problems with this commit so revert it for
now.

Link: https://lore.kernel.org/r/202501221029.fb0d574d-lkp@intel.com
Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-lkp/202501221029.fb0d574d-lkp@intel.com
Cc: John Ogness 
Cc: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

Merge 6.13-rc7 into tty-next

2025-01-13T05:46:26+00:00

We need the serial driver fixes in here to build on top of.

Signed-off-by: Greg Kroah-Hartman

serial: 8250: Revert "drop lockdep annotation from serial8250_clear_IER()"

2025-01-10T15:08:25+00:00

The 8250 driver no longer depends on @oops_in_progress and
will no longer violate the port->lock locking constraints.

This reverts commit 3d9e6f556e235ddcdc9f73600fdd46fe1736b090.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20250107212702.169493-7-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman

serial: 8250: Switch to nbcon console

2025-01-10T15:08:25+00:00

Implement the necessary callbacks to switch the 8250 console driver
to perform as an nbcon console.

Add implementations for the nbcon console callbacks:

  ->write_atomic()
  ->write_thread()
  ->device_lock()
  ->device_unlock()

and add CON_NBCON to the initial @flags.

All register access in the callbacks are within unsafe sections.
The ->write_atomic() and ->write_thread() callbacks allow safe
handover/takeover per byte and add a preceding newline if they
take over from another context mid-line.

For the ->write_atomic() callback, a new irq_work is used to defer
modem control since it may be called from a context that does not
allow waking up tasks.

Note: A new __serial8250_clear_IER() is introduced for direct
clearing of UART_IER. This will allow to restore the lockdep
check to serial8250_clear_IER() in a follow-up commit.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Tested-by: Petr Mladek 
Link: https://lore.kernel.org/r/20250107212702.169493-6-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman

serial: 8250: Provide flag for IER toggling for RS485

2025-01-10T15:08:25+00:00

For RS485 mode, if SER_RS485_RX_DURING_TX is not available, the
console ->write() callback needs to enable/disable Tx. It does
this by calling the ->rs485_start_tx() and ->rs485_stop_tx()
callbacks. However, some of these callbacks also disable/enable
interrupts and makes power management calls. This causes 2
problems for console writing:

1. A console write can occur in contexts that are illegal for
   pm_runtime_*(). It is not even necessary for console writing
   to use pm_runtime_*() because a console already does this in
   serial8250_console_setup() and serial8250_console_exit().

2. The console ->write() callback already handles
   disabling/enabling the interrupts by properly restoring the
   previous IER value.

Add an argument @toggle_ier to the ->rs485_start_tx() and
->rs485_stop_tx() callbacks to specify if they may disable/enable
receive interrupts while using pm_runtime_*(). Console writing
will not allow the toggling.

For all call sites other than console writing there is no
functional change.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20250107212702.169493-5-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman